A master-oscillator power-amplifier transmitter has been operating normally. The antenna ammeter suddenly reads zero. All filaments are burning and plate and grid meters read normal currents and voltages. What happened?
• Behavior of a master-oscillator power-amplifier (MOPA) when the RF output path is interrupted • Difference between an actual loss of RF current in the antenna and a fault in the measuring circuit (meter or leads) • What it means when all filaments, plate, and grid readings remain normal
• If the transmitter is still producing RF power normally, what would you expect to see on the antenna ammeter under normal conditions? • If the antenna current suddenly reads zero but all other transmitter indications are normal, is it more likely that the RF stopped or that the indication of RF stopped? Why? • Which choices refer to problems with the RF system itself, and which refer only to problems in how it is being measured or indicated?
• Confirm that normal plate and grid readings usually indicate the RF stages are functioning properly • Think about whether a shorted ammeter would force current to zero or simply bypass the meter movement • Consider how an open circuit in the remote-reading meter leads would affect the meter indication while leaving transmitter operation unchanged
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